2006 TASAE Paper by K.Roy

Water Resources in relation to Major Agro-Environmental Issues in Japan
Kingshuk Roy
College of Bioresource Sciences, Nihon University
1866 Kameino, Fujisawa-shi, Kanagawa 252-8510, Japan
royk@brs.nihon-u.ac.jp
Abstract
Although Japan is well known as an industrialized country rather than an agricultural one,
agriculture is treated as a very important sector for its cultural and environmental perspectives.
Only 15% of Japan's land is suitable for cultivation, but the agricultural economy is highly
subsidized and protected. With per unit area crop yields among the highest in the world,
agriculture sector still dominates the major part of water use (65%) in Japan followed bydomestic and industrial uses (20% and 15% respectively). Like many other monsoon Asian
countries, rice is the staple food in Japan, and paddy fields and terraces are often referred to as
the country’s cultural and environmental indicators. This paper outlines the condition of water
resources and their relations to some major agro-environmental issues in Japan.
Keywords: water use, water pollution, surface runoff, agro-environment, agro-ecosystem.
INTRODUCTION
Agriculture plays a significant role in the world in achieving sustainable development
because of its importance to food supply and the social structure of rural areas, as well as its
impact on nature and the environment. Depending on the region/country, these different aspects
are weighted differently. As for Japan, the country’s agriculture, although a tiny but often
termed as an outstanding contributing sector to the country’s economy (1.5% of GDP) , ischaracterized by high production and secured subsidies because of its socio-cultural backgroundand environmental characteristics. The relatively wet climate dominated by monsoon provides
the country with considerable freshwater supplies. The general reliability of the precipitation
pattern, coupled with Japan's extensive network of rivers is used for irrigation, make possible
extensive wet-rice cultivation. For the last two decades, the country has been paying muchattention for its water resource management as well as on agriculture and environmental aspects.
However, some natural and man-made agro-environmental disasters associated with water (useand quality), land (use and management), agro-ecosystem, agro-biodiversity, global warming etc.
still remain as major problems to be solved. This paper reviews some major agro-environmental
issues in relation to water resources management in Japan. The main objectives of the paper areto:○ introduce the present status of water resources, such as precipitation, rivers & lakes, water
withdrawal rate in Japan;○ Review the linkages between water and some major agro-environmental issues, such as nonpoint source pollution, soil erosion, ecosystem and biodiversity;○ Highlight a case study in southern part of Japan;○ Outline limitations and analyze future trends of water resources and their relation to agroenvironment ecosystem from local perspective.
The first half of the text of this review paper is composed of the information and data
available in recent publications, while the second half describes a case study and analyticalcomments.

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2006 TASAE Paper by K.Roy

CLIMATE AND GEOGRAPHICAL FACTORSJapan consists of a great string of islands in a northeast-southwest arc that stretches forapproximately 2,400 km through the western Pacific Ocean. The country has a total la nd area of
377,887 square km. Nearly this entire area is taken up by the country's four main islands; from
north to south these are Hokkaido, Honshu, Shikoku, and Kyushu. Honshu is the largest of thefour, followed in size by Hokkaido, Kyushu, and Shikoku. In addition, there are numerous
smaller islands, the major groups of which are the Ryukyu (Nansei) Islands (including the islandof Okinawa) to the south and west of Kyushu and the Izu, Bonin (Ogasawara), and Volcano(Kazan) islands to the south and east of central Honshu. About 70-80% of the country ismountainous. The mean annual precipitation is 1,740 mm (approx.), ranging from 800 mm(approx.) in the north of Hokkaido Island to 3,600 mm (approx.) in the south of the country.
Most parts of Japan are within the North Temperate Zone with four seasons a year. Though
Japan would appear to have plentiful water resources, it is so densely populated that the annual
amount of per capita rainwater is only 5,100 m³ which is about one-fourth of the world annual
average(22,000 m³/capita). Moreover, this amount varies significantly with area and time.
WATER RESOURCES IN JAPANRivers , Lakes and Reservoirs : In Japan, there are more than 2,700 river basins. Among them,
109 rivers are designated as being managed by the central government in principle because of
their major importance to the economy and to the protection of the environment. The catchment
area of these Class A rivers covers about 239,900 km². Class B rivers consist of the other rivers
which are managed at local level (prefecture government level). Average surface water
resources are estimated at 420 km³/year. There are 247 freshwater aquifers underlying a total
area of 69,130 km². The renewable potential of groundwater resources is estimated at about 27
km³/year, though because of the steep slopes, a significant part (estimated at 17 km³/year)
probably returns to the river system. Where land subsidence, saline intrusion and excessive
lowering of the water table have occurred, groundwater use has been restricted to a safe yield byapplying legal regulations and ordinances to critical areas. The total annual renewable water
resources are estimated at 430 km³/year.
More than 600 lakes are scattered among the seaside districts and the volcanic zones. The
major lakes in the country are:l Biwa lake, which lies in the inland basin near Kyoto in central-west Honshu with an areaof 674 km² and a water volume of 27.5 km³;l Kasumigaura lake, which is close to the mouth of the Tone-gawain with an area of 220
km² and a water volume of 0.848 km³;
l Inawashiro lake, which is a lake created after a volcanic eruption in northwest Honshu
with an area of 104.8 km² and a water volume of 3.86 km³.
The history of dams and reservoirs in Japan dates back many centuries, and a number ofancient earthen dams are still used for paddy irrigation. Since the 1920s, technological advances
have led to the construction of dams and weirs with modern designs, and these have contributed
mainly to irrigation development and hydropower generation. The construction of large-scale
multipurpose dams including flood control began in the 1950s to meet increasing water demand
for municipal and industrial use as well as irrigation. In 1993, there were 2,556 dams over 15 mhigh in service for water supply, hydropower generation and flood control, for a total effective
storage capacity of 16.5 km³. In addition, 587 dams under construction at that time wereplanned to provide 7.7km³. The total storage capacity of all these dams is about 29 km³. A 1990
survey showed that another 4.8 km³ were provided by small dams. In 1996, the installedcapacity of all power plants in operation was 226,994 MW, of which 21,171 MW or 19 percent
was hydropower.

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2006 TASAE Paper by K.Roy

Water Use in Agriculture : Agriculture holds the major part of water use in Japan (65% of thetotal water withdrawal). Water for flooded rice paddy fields and fish culture comprises most ofJapan’s agricultural water use. Water use for agriculture has recently been flat nationwide, witha slight decrease in ric e paddy irrigation offset by an increase in irrigation for other crops.
Irrigation of rice paddies, which takes up the largest portion of agricultural water usage, dropped
only slightly, in spite of decreased rice paddy acreage, partly because of the increased water use
per unit area in paddies and the lower rate of recycling due to the digging of separate canals for
irrigation and drainage. Demand for water in rice paddies is seen from mid-April throughSeptember, with peaks during tillage before the crop is transplanted, and in the season after
midsummer drainage. Water use during tillage in particular, has risen recently. There is a small
demand for water during seasons other than the ones mentioned above, for secondary crop
farming and crop rotation. Irrigation for other types of crops is expected to continue to increase
because the area land with access to irrigation is increasing and in many cases, agriculturalchemicals and fertilizers are mixed with the water that is used to irrigate these fields. The supply
or water to green-houses particularly, has increased steadily in recent years, and their growing
popularity has increased the demand for water in winter.
Water usage in livestock farming is expected to continue to increase because of the growth in
the number of livestock. Aquaculture is also growing, although it accounts for a small portion of
all agricultural land. Water culture, which is a form of liquid culture, is the main form of liquid
culture in terms total area. Irrigation channels have traditionally served several functions inagricultural areas, such as supplying water to wash crops and agricultural machinery, fire
protection and preservation of the rural environment. To maintain and promote the use of suchfunctions, various approaches are being taken in the improvement of irrigation channels, including
construction of recreational areas, with trees and shrubs planted along irrigation channels.
MAJOR ISSUES CONCERNING WATER AND AGRO ENVIRONMENTAs it could be understood from the above information also, to maintain the standard of quality,
to secure the required quantity, and to manage such a vast amount of fresh water used inagricultural purposes in sustainable ways are very important to maintain different related
agro-environmental components.
In this section, the author will focus and discuss some major agro-environmental problems
associated with water resource management, namely non point source pollution fromagricultural fields, rainfall erosion and its effect on aquatic ecosystem and biodiversity in southpart of the country.
Non Point Source Pollution: Water quality is a major environmental issue. Japan's aquatic
environment has improved significantly over the last few decades, as industrial water pollution
was sharply curtailed. However, the environmental quality standards for organic water pollution
are still not being met in about 30% of Japan's total water area. Pollution from non point sources
is one of the single largest remaining sources of water quality impairments in Japan. Agriculture
is a major source of several non point source pollutants including nutrients, sediment, pesticides,
and salts that deteriorate the water quality in rivers and oceans, cause eutrophication in lakes
and reservoirs.
Although in Japan, there is no general law encompassing all aspects of water resourcesmanagement, however, specific aspects related to water resources management are regulated bylegislations such as Water Pollution Control Law (updated as 1of 1996), the River law (updated
as of 1997), the Land Improvement Law (updated as of 2001), the Water Resources
Development Law (updated as of 1983) etc. Such laws have been effective to solve a specificland and water pollution problem. But when different types of pollutants come from different
non specific sites especially where farmers and non-farmers living alongside each other inagricultural and rural communities, it becomes a hard job to solve, practically.

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2006 TASAE Paper by K.Roy

Scientists in Japan have recently suggested approaches and models for proper watershedmanagement to reduce the non point effluents to the rivers and lakes. Kato et al (2004) assessed
the non point outflow loads to Kasumigaura lake for the past 10 years, and developed a material
cycle evaluating system that could reduce the total nitrogen load to the lake up to 40%.
Funakawa et al (2004) developed another water quality model based on the study of non point
effluents to Biwa lake and Noda Lagoon. Tada et al (2006) reviewed different models toestimate the effluent loads from watershed, and focused on the uncertainties of hindered nonpoint sources. According to the water quality researchers in Japan including Tada (2006) , a
model based official program, for example, the TMDL (Total Daily Maximum Load) programin USA, would be effective to reduce the effluents from watersheds to the water basins.
Soil Erosion: The outflow of topsoil from the farmlands mainly due to water and wind aretermed as soil erosion in agriculture. In Japan, soil erosion has not been a serious problem forthe last few decades except some parts of the country. Northern parts including Hokkaido andNortheast region (Tohoku region) are little vulnerable to wind erosion followed by watererosion. However, since the country has not a distinct dry season and most of the farmlands arewell reclaimed, wind erosion in Japan is an issue of merely local importance. Rather, watererosion caused by rainfall has been a long time problem (since 1972) in the south part (Okinawa
Island) of Japan. The island’s annual rainfall amounts much higher than the country’s averageannual rainfall. Moreover, farmland soils (Kunigami Maji, Shimajiri Maji, Kutcha etc.) aremostly clayey, and so vulnerable to erosion. In addition, pineapple and sugarcane are thecommon crops cultivated as the main cash crops in the island. Both these cropping fields are, by
their nature (ridged and furrowed), susceptible to erosion. In past years, many researches(Onaga et al 1978-1984, Gibo et al 1984) have been carried out that encouraged the local
government to introduce a policy named ‘Red soil pollution monitoring’ in 1985. Till today, themonitoring system is in progress, but achieved a little in practice. Further research works weredone by researchers (Onaga et al 1990, Gibo et al 1994, Kusaka et al 1998, Yoshinaga et al2000) to find out different technologies to prevent soil erosion from farmlands. Researches arestill going on this subject but if we look at the history and the present status of red soil erosion
in Okinawa, researchers’ suggestions have not always welcomed by the local farmers because ofmany locally oriented socio-cultural and traditional backgrounds (Matsumoto and Roy, 2004).
The situation reminds the necessity of doing more researches that could be accepted by the local
farmers. In other words, while planning a research, a pre-feasibility study is a must where local
farmers’ opinion gets priority.
Agro-Ecosystem and Biodiversity: Especially, in Japan, conservation of biodiversity andecosystems in agriculture has been an important issue in agricultural and environmental policy
since 1999, when a changed agricultural foundation law stimulated progress by the Japanese
government and EU (European Union). Rice paddy fields ecosystem is treated as the mostimportant agro-ecosystem and biodiversity indicator in Japan. According to the literature before,
about 2,000 species of plants and animals associated with rice paddy fields have been recordedin Japan (Hidaka 1998). This biodiversity in species richness can be regarded as a generalcharacteristic in the rice paddy ecosystem. Kobayashi et al (1973) examined in detail thebiodiversity of arthropods using sweeping methods in rice paddies of several sites of Tokushima
Prefecture in the late 1950s. More than 450 species of insects, spiders, and mites were recorded.
Kasahara (1947) examined a list of rice paddy weed specimens in 25 prefectures over Japan andrecorded 174 plant species. However, nowadays, if we had a chance to examine arthropod faunain the same fields, it might be difficult to collect a closed number of species in rice paddies suchas in the 1950s (Hidaka 2004). Such a decreasing tendency of different natural habitats andspecies in the rice field ecosystem in Japan is apparently derived from rapid urbanization, steadyproduction level maintenance etc.

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2006 TASAE Paper by K.Roy

ENVIRONMENTAL DEGRADATION BY SURFACE RUNOFF - A Case Study in
Okinawa Island –Okinawa is Japan’s southernmost prefecture and consists of hundreds of islands in a chain
over 1,000 km long where Okinawa Island is the largest one. Okinawa has a humid subtropicalclimate, with an annual rainfall ranging from 2,000 to 2,500mm. The rainfall erosivity is very
high and the dominant soils (commonly termed as red soil) are highly erodible that causes theloss of valuable topsoil from the farmlands as well as making the ocean water polluted. Most of
the red soil particles (mostly silt and clay) carried to the sea by rivers and or canals aredeposited on semi enclosed reef moats adjacent to the coast, and often the red soil is repetitively
stirred up by turbulence induced by typhoons and monsoons. The water then becomes cloudy
and the soil is distributed over the reefs and cause decay. The deterioration of the coral reefalong with other aquatic species environment as a result of eutrophication and pollution fromincreasing sedimentation has already been reported. Coral reefs, which offer shelter to small
reef animals in their three-dimensional spaces, are said to hold the largest number of species perunit area on earth. So, when corals die out and the three-dimensional space decreases,
eventually the numbers of fish and other organisms also decrease. The central and local
government offices have introduced several techniques such as establishment of green belt,
infiltration tank, sedimentation tank, underground drainage etc. and uses of different soil
improvers, coagulants, mulches etc., as well as evaluation and monitoring system for measuring
red soil outflow. However, things are not going satisfactorily as expected. The reason is that a
lot of local factors other than technological aspects are involved in the red soil erosion process
in Okinawa. But one thing what farmers and policy makers agree is that – ‘not to let the soil goout of the fields is the best way to overcome the situation’.
For the last few years, the author has been carrying out field surveys and experiments in someparts in Okinawa to find out some technologies that could be accepted by the local farmers. In
this section, the author will introduce a case study result to improve the hydraulic conductivityof red soil while treated with different waste materials. As also mentioned in the above sectionof soil erosion, most of the Okinawa’s farmland soils are clayey and silty with poor hydraulicconductivity. When raindrops strike the surface, the surface soil creates a crust which also
hampers the infiltration. As a result, surface runoff takes away the topsoil out of the field.
Therefore, to increase the infiltration rate would help to decrease the surface runoff. A
preliminary survey was carried out to get an idea about the technology extension among thefarmers in Okinawa. The survey result helped the author and his research group to make adecision to grasp the present condition of conservation works in Okinawa’s farmlands andsearch for possible locally fitted materials. In most of the sugarcane and pineapple fields,
farmers use the plant residues as organic mulch. This practice helps to maintain the soil
moisture as well as to minimize the raindrop effect to some extent. But when heavy andconcentrated rainfall occurs, the mulching materials themselves also washed out from the fields.
Therefore, while planning the research and experiments, the author targeted to find out more
efficient ways to use the plant residues so that it could be a contributing factor to improve thesoil structure (like humus) that accelerates infiltration rate. Discarded fired potteries, a common
traditional item, were also used as experimental materials. The materials were processed in theauthor ’s lab. The processed materials were then mixed in different ratios with the sampled redsoil (Kunigami Maji soil), and put them (only sugarcane residue-mixed samples) in an artificial
atmospheric chamber (Fig. 1). The temperature and the humidity of the artificial atmosphericchamber were fixed to that of Okinawa’s condition. In short, the materials (sugarcane plant
residues and fired potteries) were grinded by a small grinder, and then mixed them withdifferent ratios (soil: mixed material). Then the mixed soil samples were placed in the artificial
chamber for 1 month, 2 months, 3 months and 4 months. Observations were carried out
regularly and column tests (Fig. 2) were performed by using the treated soil samples. Thechanges in organic matter content (%), thickness of crust (mm), porosity (%), soil aggregation,

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2006 TASAE Paper by K.Roy

and hydraulic conductivity (cm/s) were measured for each soil sample . From the result, the best
condition to use the local materials was determined. The results (Fig. 3 and 4, Table 1 and 2) ofthe experiments indicate that a small amount of grinded sugarcane plant residues mixed with thered soil could increase the infiltration rate that could result a decrease of surface runoff. Such atreatment can easily be performed under natural condition in any Okinawa’s farmland just likemaking a hole at one corner of the field and put the grinded residues inside it. It is noted here thatwhile applying the result to the practical farmlands in Okinawa, a machine to perform the grinding
operation in large scale has to be designed.
CONCLUSIONS
When many of the Asian countries are still struggling to provide the basic needs to theirpeople, factors such as population, poverty, education, technology are not issues in Japan. The
Japanese Government and its Ministries are doing a lot of research and extension works within
the country and providing various materials, incentives and programs to help people understandthe current state of the agro-environment and water resource. Japan is one of the most leading
countries in the world now to handle the environment and water problems. The country hosted
the Ministerial Conference, on the occasion of the 3rd World Water Forum, in 2003. ‘Kyoto
Protocol’ was highly appraised by the environment lovers throughout the world. Even after that,the speed to eradicate the existing and remaining tasks as some mentioned in this review paper
is not notably rapid as and when compared with the same to the industrialization and economic
development of the country. Why? As to the author ’s opinion, many other factors such associo-cultural, traditional, after-effects of modernization etc. are correlated with the resource
management and environmental aspects. Some of them are concluded here.
Recently (2003), Japan Government adopted a policy to establish a sound hydrological cycle
via various fields such as forests, agricultural land, rivers, water-supply and sewerage systems,
etc. Five ministries (Ministry of Health; Ministry of Agriculture; Ministry of Economy;
Ministry of Land, and Ministry of Environment) have been engaging in consultative meetings inorder to share related information and promote deliberation on comprehensive measures. The
Guideline for Establishment of Sound Water Cycle (2003) has been developed to clarify thebasic direction of identifying the factors that cause water-related issues by evaluating the overallwater cycle, and dealing with the problem. The policy is undoubtedly a good step. But, as alsosuggested by many researchers in Japan, still no efficient model or program like TMDL (Total
Maximum Daily Load) program (in USA) was included in the government policies and lawsthat could assess and prevent the non point effluents from any particular spot more efficiently.
As for soil erosion problem in Okinawa, less pre-feasibility studies were carried out on thelocal farmers’ attitude before introducing technologies to prevent farmlands from soil loss.
Agriculture and farming works are labor-intensive. In Okinawa, most of the farmers prefer toproduce sugarcanes and pineapples because the lands are suitable for that crops as well as thefarming operations, land management are less labor intensive. In addition, no other majoralternative crops have been proved more economically feasible there. Replacing the existing
traditional farming system/crops by only a technologically-better way is mostly impractical in
Okinawa. Therefore, to extend any new method to the farmers, locally fitted research works
should be given priority.
There are many reports and media-news on the recent food habit change of young Japanese.
Western foods, fast-foods that not essentially use rice materials are getting popular and theconsumption of Japanese rice is getting low gradually. Moreover, young generation is losing
fascination to agricultural works. Naturally, the paddy field area is showing a declining
tendency in recent years. Labor shortage is so acute that Japanese Government is considering toimport foreign labors for agricultural works (Asia Times, Dec 3, 2003). In Japan, where rice
paddy field is the ma in indicator of agro-environment and ecosystem, paddy-less Japan willbring many new environmental problems.

62006 TASAE Paper by K.Roy

Besides, there are some other problems associated with water and agro-environment still
remain to be solved, such as construction of dams, land consolidation, river head works, global
warming etc. Whenever any of these technical matters becomes a problem in any locality, andfocused in the mass media, rather than technical, many socio-cultural, political and traditional
factors are in the headlines. So, why not such factors should be considered at the basic stage
while planning and designing a technological approach?
Finally, it is fact that every short of eco-environmental problems associated with water andagriculture cannot be eradicated completely (100%) since the total ecosystem is incorporated
with many known and unknown sub eco-systems and factors. But in a highly developed country
like Japan where government and people are careful, resource management and maintenance of
eco-environment can be achieved to the best.
ACKNOWLEDGEMENTS
The author would like to express his gratitude to the TASAE organizers. Thanks are due tothe organizing committee secretary general Dr. Hideo Hasegawa. Special thanks to Dr. Sadao
Nagasaka of Nihon University for his suggestions while making this paper.

References
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Chapter-2, pp64-68 (2002).
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as mixed materials-, Proc. of the national conference of Japanese Society of Irrigation,
Drainage and Reclamation Society (JSIDRE), pp.766-767, (2006) (in Japanese)
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Conservation Extension - from concepts to adoption- , published by SWCST, pp. 47-50(1996)
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Figures and Tables in this page show the experiment results as stated in the section:「ENVIRONMENTAL DEGRADATION BY SURFACE RUNOFF- A Case Study in Okinawa Island –」Fig.1 Artificial Atmospheric Chamber

Fig.2 Hydraulic Conductivity Test Apparatus

Porosity(%)

n

Table 1 Organic Matter in Treated Soil
74
72
70
68
66
64
62
60
58
56
54
Control 2months

Sugarcane residues

OMC（
%)

2 months treatment

6.62

3 months treatment

6.63

4 months treatment

7.56

3months 4months

Treatment

Fig.3 Comparison of Porosity (%)
Table 2 Crust Formation in Each Sample

7

Thickness(mm)Value of a

Sample865Control

3.4

Sugarcane(non-treated)

2.5

Sugarcane(2 months treated)

1.5

Sugarcane(3 months treated)

1.6

2

Sugarcane(4 months treated)

1.5

1Fired potteries（
0.2〜2mm)

2.1

Fired potteries（
2〜4mm)

2.5

4
3

Co
ntr
ol

Su
ga
rca
ne
(no
n
)
Su
gar
can
e(2
mo
nth
)
Su
ga
rca
ne
(3m
on
th)
Po
tte
ry(
0.2
〜
2m
Po
m)
tte
ry(
2
〜
4m
m)

0

Treatment

Fig.4 Comparison of Hydraulic Conductivity(cm/s)* when, hydraulic conductivity k=a×10-4 (Darcy’s Law)8